I live in one of my fathers houses as a tenant and 5 years ago asked a girlfriend & her daughter to move in. the relationship has been on the rocks for a while now and I have asked her to leave several times which she refuses to do. How do I get her out. I don't really want to involve my father (the landlord) as he has become friendly with her dad and I don't want to ruin their friendship. Please help

This is going to be tough, since most likely she is reconised as a joint tenant. Even your father may have some trouble, since what legal grounds would he use to evict her>

Sounds like time for an attorney locally on this one.
Better info if you answer some of these
1. is there a wrtten rental or lease agreement
a. if so, whose names are on it
2. has she been helping paying bills at the house.

What legal grounds for evicting would you plan on using ?